3-D nanoscale changes in rechargeable battery anode

Scientists at DOE's Brookhaven Lab have made the first 3-D observations of how the structure of a lithium-ion battery anode evolves at the nanoscale in a real battery cell as it discharges and recharges. The details of this research could point to new ways to engineer battery materials to increase the capacity and lifetime of rechargeable batteries.

“This work offers a direct way to look inside the electrochemical reaction of batteries at the nanoscale to better understand the mechanism of structural degradation that occurs during a battery's charge/discharge cycles,” said Brookhaven physicist Jun Wang, who led the research.

To capture the images, the scientists built a tiny battery cell measuring less than one millimeter containing all battery components—the electrode being studied, a liquid electrolyte, and the counter electrode—supported by relatively transparent materials to allow transmission of x-rays, and properly sealed to ensure that the cell would work normally and be stable for repeated cycling. They placed the cell in the path of high-intensity x-ray beams generated at beamline X8C of Brookhaven's National Synchrotron Light Source (NSLS). More than 1400 two-dimensional x-ray images of the anode material with a resolution of approximately 30 nanometers were later reconstructed into 3-D images—much like a medical CT scan but with nanometer-scale clarity.

The images revealed that the particles making up the tin-based anode developed significant curvatures during the early charge/discharge cycles, leading to high stress. “We propose that this high stress led to fracture and pulverization of the anode material,” Wang said. “Our study will improve understanding of how this happens and help us develop better controls.”